1. Field of the invention
The present invention relates to an optical pickup apparatus that is preferably used when at least either a process of reading information recorded in an optical recording medium or a process of recording information onto the optical recording medium is performed.
2. Description of the related art
FIG. 6 is a view showing a configuration illustrating an optical pickup apparatus 1 according to the related art. The optical pickup apparatus 1 is constituted to include a light source 2, a beam splitting diffraction grating 3, a hologram diffraction grating 4, aperture limiting means 5, a collimating lens 6, an objective lens 7, and a photodetector 8. A laser beam emitted from the light source 2 is transmitted through the beam splitting diffraction grating 3, the hologram diffraction grating 4, and the aperture limiting means 5, and then transmitted through the collimating lens 6 and the objective lens 7, and condensed on an information recording surface of a disk-shaped optical recording medium (hereinafter referred to as an “optical recording medium”) 9. The laser beam reflected by the information recording surface of the optical recording medium 9 is transmitted through the objective lens 7, the collimating lens 6, and the aperture limiting means 5, and then is diffracted by the hologram diffraction grating 4, and then enters the photodetector 8, to read a signal.
The optical pickup apparatus 1 is constituted by providing the aperture limiting means 5 so as to prevent reflected light reflected by optical components such as the collimating lens 6 and a laser beam that is not condensed on the information recording surface of the optical recording medium 9, of a laser beam emitted from the light source 2, from entering the photodetector 8. Technologies similar to such optical pickup apparatus 1 have been disclosed in for example Japanese Unexamined Patent Publication JP-A 10-208294 (1998), and Japanese Unexamined Patent Publication JP-A 11-344666 (1999).
An optical head apparatus disclosed in JP-A 10-208294 (1998) is constituted by providing aperture limiting means in a diffraction element so as to reduce amounts of diffracted light beams on an approach route which diffracted light beams are generated when a light beam emitted from a light source enters the diffraction element before reaching condensing optics, and to prevent the diffracted light beams on the approach route from entering an light-receiving element by being reflected by an optical recording medium.
An optical pickup disclosed in JP-A 11-344666 (1999) is constituted by providing, for example aperture limiting means between a beam splitting section for splitting two laser beams having different wavelengths and a laser/detector integrated unit, so as to remove flare which enters a light-receiving element.
In the optical pickup apparatus 1 as described above, the optical head apparatus in JP-A 10-208294, and the optical pickup in JP-A 11-344666, there arises a problem in which by providing the aperture limiting means, reflected light in a laser beam emitted from the light source is newly generated which is reflected on a surface facing the light source of the aperture limiting means and the reflected light enters the photodetector or the light-receiving element to serve as noise, thus preventing detection of a correct signal. Technologies to solve this problem have been disclosed in, for example JP-A 2005-216458 and JP-A 11-25496 (1999).
An optical pickup apparatus disclosed in JP-A 2005-216458 is constituted by providing a light shielding aperture in which an undesired light guide surface having a curved surface shape is formed to guide undesired light in another direction from a direction toward a photodetector, so as to guide the undesired light in another direction from a direction toward the photodetector and thus prevent the undesired light from entering the photodetector.
An optical pickup apparatus disclosed in JP-A 11-25496 is constituted by providing an aperture, on an optical base for arranging optical components including a light-receiving/light-emitting integral element, at a position on an output optical path from the light-receiving/light-emitting integral element, having an aperture having a diameter substantially identical to a necessary light flux diameter, and being constituted by a transparent thin plate composed of sheet metal, glass, or resin for shielding light out of the necessary light flux diameter, so as to suppress or prevent stray light around a signal-detecting/light-receiving region of a photodetector. In addition, the optical head is constituted by providing, in the light-receiving/light-emitting integral element, an aperture region for transmitting only a necessary light flux to a light incoming/outgoing surface, and by further providing, in a region other than the aperture region, various kinds of antireflection, scatter reflection absorption, or light absorption functions, such as addition of an antireflection coating, satin finish treatment, or the like, so as to further reduce the stray light around the signal-detecting/light-receiving region.
The optical pickup apparatus disclosed in JP-A 2005-216458 is constituted by providing the light shielding aperture in which the undesired light guide surface is formed, so as to guide the undesired light in another direction from a direction toward the photodetector. However, it is difficult to prevent a portion of a laser beam out of an effective diameter of an objective lens and having relatively high light intensity, from entering a hologram diffraction grating and the photodetector. And when the laser beam reflected by an optical recording medium once enters the hologram diffraction grating, the laser beam tends to enter the photodetector. Accordingly, there arises a problem that a correct signal cannot be detected.
Furthermore, in the optical pickup apparatus disclosed in JP-A 2005-216458, it is necessary to achieve a high-accuracy positioning of aperture limiting means from a light source, resulting that it is difficult to assemble and adjust the optical pickup apparatus. Accordingly, there has been arisen a problem in which it is difficult to improve productivity of the optical pickup apparatus, thus increasing manufacturing costs thereof.
Further, when various kinds of antireflection, scatter reflection absorption, or light absorption functions, such as addition of an antireflection coating, satin finish treatment, or the like, are provided in a region other than the aperture region of the signal-detecting/light receiving region, as an optical head disclosed in JP-A 11-25496, reflected light can be reduced, but cannot be prevented completely. Therefore, there arises a problem in which the reflected light enters the photodetector, thus preventing detection of a correct signal.